1. Field of the Invention
The present invention relates to compositions and methods for the protection of vision from incident electromagnetic radiation using plasmon resonant particles. More particularly, the invention relates to infrared radiation extinguishing eye protection and a process for producing infrared radiation extinguishing eye protection utilizing plasmon resonant particles. Most particularly, the invention relates to infrared radiation extinguishing contact lenses and a process for producing infrared radiation extinguishing contact lenses utilizing optically tunable nanoshells.
2. Prior Art
Eye exposure to certain portions of the electromagnetic spectrum is known to be damaging to the cornea and to be the cause of several ocular pathologies. More specifically, while the visible light portion of the spectrum ranges from approximately 400-700 nm, those portions of the energy spectrum adjacent to visible light, namely ultraviolet radiation (approximately 200-400 nm), and infrared radiation (approximately 670-1200 nm) are known to be harmful to the eyes.
The need for these eye protection devices results from the hazard to the eye from extended exposure to solar radiation (either at sea level, at other altitudes or in space) or artificially generated electromagnetic radiation, such as lasers. Broad protection from the solar radiation can be effected by devices that provide substantial extinction across many wavelengths. The focusing mechanism of the eye will concentrate incident light on the retina. This focusing effect can result in retinal damage, either temporary or permanent, from electromagnetic radiation. If the incident electromagnetic radiation is not visible to the eye, such as in the near infrared, damage can occur without awareness of the incident light.
Devices for protecting the eye from incident light include goggles, glasses, contact lenses and similar devices. Moreover, certain devices have been designed and developed to extinguish ultra-violet, visible, near-infrared or other wavelengths.
Generally, films, reflective surfaces or additives have been used in these devices to alter eye color or appearance by selectively reflecting or absorbing different wavelengths. Additionally, these techniques have been used to selectively diminish or extinguish some or most of the incident light across a broad area of the solar spectrum, such as in traditional sunglasses.
One area where exposure to infrared radiation is of particular concern is through the use of lasers in military applications. The current most common laser eye protection is goggles. However, when used by combat forces, goggles can pose integration problems by interfering with other equipment. In many cases, it is difficult or impractical to integrate such goggles with these other pieces of equipment, and the use of goggles or glasses allows the potential for reflected incident electromagnetic radiation to reach the eye. These integration issues have led many soldiers who require traditional vision corrective glasses to wear contact lenses. Therefore, it would be desirable to provide contact lenses that are capable of extinguishing infrared radiation.
Considerable attention has focused in the prior art on providing glasses and contact lenses capable of absorbing or reflecting ultraviolet radiation in order to protect the eyes. In particular, it is well known in the art to add UV-absorbing compounds to a contact lens polymer or to otherwise provide a dye or color additive to the lens in order to block ultraviolet light. Heretofore, little attention in the prior art has focused on protecting the eyes from infrared radiation. Part of this is due to the fact that normal eye exposure to infrared radiation is much less intense than eye exposure to ultraviolet radiation. Shorter wavelengths have higher energy levels and are more commonly absorbed by human tissue, resulting in a higher potential for damage. Infrared radiation in solar radiation has a lower level of intensity as well as a lower energy level, and generally is less damaging to the eye or tissue. Higher intensity infrared radiation is most commonly associated with lasers. Moreover, unlike UV-absorbing agents, there are very few substances known to absorb infrared radiation and remain relatively transparent in the visible. Those skilled in the art will understand that while carbon does in fact absorb infrared radiation, it is otherwise undesirable because it also absorbs light from other parts of the energy spectrum, including visible light, therefore reducing the ability to selectively extinguish certain wavelengths while maintaining transmission in other wavelengths.
Colored or tinted contact lenses are commonly used to alter eye color for cosmetic reasons, but do not offer selective wavelength protection. Tinted lenses employ dyes or other additives to provide color without completely blocking the passage of visible wavelengths through the lens. These techniques are generally designed to avoid coloration of the pupil to create a natural appearance. Examples of these lenses are described in U.S. Pat. Nos. 4,468,229; 4,460,523, 4,447,474; 4,355,135; 4,252,421; 4,157,892; 3,962,505; 3,679,504 and 2,524,811.
Reflective coatings have also been described to reflect specific wavelengths to provide a color change to the iris of the eye, an example of which is described in U.S. Pat. No. 6,164,777.
U.S. Pat. No. 4,669,834 describes the use of reflective material to protect the eye from electromagnetic radiation, including infrared wavelengths, wherein such reflective material included metal particles, such as gold, platinum, stainless steel, silver, nickel, chrome, aluminum, and nickel alloys; other particulate matter, including ground oyster shells and mica. The specifications do not provide the optical properties of the materials described, which are well-known to provide the most significant extinction in the visible spectrum. In general, these metal particles have a plasmon resonance and will extinguish light principally in the visible wavelengths. The extinction properties of these particles are generally narrow, if the particle is smaller than the incident wavelength, or broad across the visible spectrum if the particle is large. The construction of particular plasmon resonant particle using these materials to extinguish selective wavelengths was not described.
U.S. Pat. No. 5,112,883 describes the use of melanin, a biological molecule, as an absorbing pigment for radiation protection. The extinction spectrum of melanin as described and as known to those of ordinary skill is principally in the visible spectrum, with limited absorption in the near infrared, and limited ability to alter the absorption spectrum if desired to selectively extinguish wavelengths.
These traditional approaches to design and manufacture of contact lenses and other protective eyewear involve protection from radiation intensities common in solar radiation and from reflection of such radiation. Some methods are used to provide protection from more intense radiation. U.S. Pat. No. 4,848,894 describes a method for eye protection from high-intensity optical radiation such as that from a laser. The invention contemplates the use of thin films, reflectors, filters or absorbing dyes. The degree and wavelength of protection described is inherent in the particular properties of the materials described.
The recent development of plasmon resonant particles can contribute significantly to the field of eye protection. While traditional protective techniques have varying levels of stability and selectivity for vision protection, plasmon resonant particles offer the ability to selectively extinguish, either by absorption or scattering, electromagnetic radiation in a broad range of the electromagnetic spectrum. Additionally, these materials can be produced in a biocompatible format to avoid damage to the eye when in close contact, such as in a contact lens format.
Plasmon resonant particles are generally metallic particles which efficiently scatter optical light elastically because of a collective resonance of the conduction electrons in the metal. The magnitude, bandwidth and extinction peak of the plasmon resonance associated with a particle are dependent on the size, shape, structure and composition of the particle. These factors are also affected by the environment in which the particle is placed. Generally, the optical properties of a plasmon resonant particle can be significantly different than solid material. For example, materials of a particular shape can have significantly different optical properties than materials of a similar shape but different size or of a similar size but different composition or of a similar shape but different composition.
As plasmon resonant particles were first manufactured, the possibility of using such materials for extinguishing selective wavelengths was contemplated. In U.S. Pat. No. 6,344,272, Oldenburg et al indicated that the selective infrared absorption of their plasmon resonant particles, metal nanoshells, may be useful for laser eye protection, or eye protection from other potentially damaging sources of infrared radiation. However, the authors did not describe the particles required for such application or the methods of preparation of the protective eyewear.
Subsequently, it has been demonstrated that plasmon resonant particles can be embedded in polymers or materials for different applications. U.S. Pat. Nos. 6,645,517 and 6,428,272 describe methods for including plasmon resonant particles in polymers for drug delivery and as a light-activated device. U.S. Pat. No. 6,852,252 describes the use of plasmon resonant particles to change the rate of photo-oxidation of polymers.
Plasmon resonant particles are available in many forms. One such form is a metal nanoshell, as more fully described in U.S. Pat. No. 6,344,272, incorporated herein by reference. Another such form is a nanorod, as described in Journal of Physical Chemistry B, Volume 103, pg. 3073, (1999). Other forms include stars (Nanoletters, Volume 6, pg. 683 (2006), cubes, elliptical particles, as described in the enormous amount of literature. For a review see Optical Properties of Metal Clusters by Kreibig and Volmer, Springer-Verlag (1995). A common trait of plasmon resonant particles is the ability to manufacture such particles to have desired optical properties, including extinguishment of electromagnetic radiation in various parts of the spectrum. Those skilled in the art will appreciate that protective eyewear may be comprised of plasmon resonant particles selected from among various sizes, shapes and compositions.
With this in mind, those skilled in the art will appreciate that a contact lens must be functional and biocompatible, with different requirements than goggles or glasses. The appropriate characteristics of a good contact lens include oxygen permeability, wettability, material strength, and stability. These factors must be carefully balanced to achieve a useable contact lens. Oxygen permeability is paramount since the cornea receives its oxygen supply exclusively from contact with the atmosphere. Tear fluid wettability keeps the contact lubricated, allowing it to be worn comfortably on the eye.
Contact lenses are typically hydrogels, a hydrated crosslinked polymeric system that contains water in an equilibrium state. In general, as the water content increases, the oxygen permeability also increases. These hydrogels are typically comprised of copolymers of N-vinyl-pyrolidone and methyl methacrylate, which have water content in the 70-80% range.
Accordingly, any modification to a contact lens to provide infrared wavelength protection must not alter the biocompatibility, wettability, or oxygen permeability. In addition, any embedded material must be stable, not oxidize, and be easily embedded in a polymeric system.